1. Field of the Disclosure
The present disclosure relates generally to scanners and more particularly to an LED illumination system for a scanner that includes an ultraviolet light emitting device.
2. Description of the Related Art
Typical contact image sensor (CIS) scanners include an illumination system having one or more light emitting diodes (LEDs). These systems often include a three channel array of red LED(s), green LED(s) and blue LED(s) (collectively, RGB LEDs). Alternatives include those where other colors in the visible spectrum are used such as orange LED(s). During a scanning operation, where a black and white scan is desired, the RGB LEDs may be illuminated simultaneously to form white light. Where a color scan is desired, the RGB LEDs may be illuminated in sequence to successively capture the red, green and blue components of the image being scanned. The scanner may then convert the individual color components into an aggregate image. LEDs are preferred to other conventional light sources, such as fluorescent lamps, because of their low energy requirements. LEDs also emit light at a constant rate as soon as they are turned on. This reduces the warm up time required in comparison with scanners utilizing fluorescent lamps.
Conventional RGB LEDs possess narrow band discrete spectrums that, in some instances, may lead to metameric failure in conventional RGB LED based scanners. Metamerism refers to the matching of the apparent color of an object with different spectral power distributions. The apparent color of an object depends on the spectral reflectance of the object as well as the spectral emittance of the light shining on it. In the case of a document or object to be scanned, the spectral reflectance of the image depends on the chemical composition of the marking material (e.g., ink, toner, etc.) and the chemical composition of the substrate (e.g., plain paper, glossy paper, fabric). For example, an inkjet print can be designed to match the color of a silver halide print when exposed to sunlight or conventional fluorescent office light even though the inkjet print and the silver halide print have different spectral reflectances due to their different chemical compositions. However, when the silver halide print and the inkjet print are subsequently scanned with a scanner that employs an RGB LED illumination system, the resultant scans may have very different colors due to differences in the spectral emittance of RGB LEDs versus sunlight/fluorescent light. As a result, the color of one or both of the scans may appear different from its corresponding original. This, in turn, may lead to customer dissatisfaction with the image quality produced by the scanner.
Given the broad range of substrates and marking materials used in printed materials (e.g., silver halide, inkjet, dye sublimation, and laser prints), it is impossible to provide a single scan color table capable of accurately reproducing the colors of the original in the scan. One solution is to provide multiple color tables each corresponding to a known original type. However, this solution requires that the scanner know the material being scanned and match it with the appropriate color table. One option is to require the user to provide an input to the scanner identifying the chemical nature of the original being scanned. This solution is undesirable because it complicates the user experience and is subject to user error thereby increasing the potential for customer dissatisfaction. Another option is to include a marking or indicia on the front or the reverse side of the material being scanned indicative of the scanner color table that should be used. However, marks on the front of an original might interfere with the content of the original and/or might be found distasteful by the customer. Further, paper manufacturers may resist adding an additional mark to their products. This option is also limited to situations where the material being scanned includes such a marking and the scanner has a sensor that is able to correctly identify the marking. This additional sensor could result in an undesirable cost increase in manufacturing the device.
Accordingly, it will be appreciated that an effective and efficient LED illumination system for a scanner that reduces the occurrence of metameric failure without requiring identification of the chemical nature of the materials being scanned is desired.